This invention relates, in general, to bond testing, and more particularly, to testing an electrical connection which is formed when a package lead is bonded to a pad area on a semiconductor device.
Increased functionality added to a semiconductor chip due to higher device densities will typically lead to an increased number of inputs and outputs. Packages are being developed to handle high numbers of inputs and outputs. Testing the integrity of bonds formed when package leads are bonded to the semiconductor chip will be critical to eliminating field failures due to defective bonds. Older methods for testing the integrity of the bonds may not work with new packages, be sufficient to insure long term reliability, or be fast enough for a production environment with high pin count packages.
For example, a high pin count package currently offered is known as a TAB package. The TAB package offers very tightly spaced leads which couple to a semiconductor device. Solder bumps are placed on pad areas of the semiconductor device. The TAB package leads align with the pad areas of the semiconductor device. The TAB leads are aligned to the pads such that a portion of the lead is placed above the solder bumps. The TAB package is lowered until the leads make contact to the solder bumps. A thermal cycle melts the solder bumps, coupling the leads to the semiconductor pads. Two interfaces are created, a TAB lead to solder bump, and solder bump to pad area, either of which could compromise quality of the device. An electrical test only confirms that a connection exists. Other methods must be used to determine the bond quality. The current test most widely used to measure a TAB bond is a destructive test. A package lead is physically separated from the solder and pad. The force needed to separate the bond is used to measure the bond integrity. By inference, the destructive test determines the quality of the remaining bonds.
It would be of some importance to provide a non-destructive method for determining the integrity of a bond. The method should be non-destructive, allow for individual bond testing, and be fast enough for use in a production environment.